The long-term goal of this proposal is to develop a Salmonella HIV-1 DNA vaccine vector that elicits humoral and cell-mediated immune responses against HIV-1, both in the mucosal and systemic immune compartments. Rationale for the development of these vectors stems from an increasing body of evidence indicating that mucosal immunity is likely to play a significant role in protection against sexually acquired HIV-1. Furthermore, although it is possible to boost mucosal responses with parenteral immunogens, induction of strong mucosal immune responses requires mucosal priming. In this vein, we have shown that intragastric vaccination with a Salmonella Env DNA vaccine vector generates Env-specific CD8+ T cells, in both mucosal and systemic lymphoid tissues. By contrast, intramuscular vaccination with the Env DNA vaccine only induces a CD8+ T cell response to Env in systemic lymphoid tissues. The central hypothesis of this proposal, therefore, is that Salmonella HIV-1 DNA vaccine vectors are more effective at priming mucosal immune responses to HIV-1 antigens, than parenteral HIV-1 DNA vaccines. We will address our central hypothesis and reach the long-term goal of this proposal by completing the following specific aims: 1. To construct DNA vaccines that co-express an HIV-1 antigen and a mucosal adjuvant; 2: Identify a Salmonella HIV-1 DNA vaccine that elicits durable humoral and cellular responses to HIV-l in the mucosal and systemic immune compartments; 3. To determine whether preexisting immunity against Salmonella reduces the immunogenicity of Salmonella HIV-1 DNA vaccine vectors; 4: To measure the immunogenicity of an array of prime-boost vaccination protocols using selected Salmonella vector constructs developed in aims 1 through 3. Overall, we believe that the studies proposed herein will further advance this vector system toward widespread clinical application in developing and developed countries.